With the continuous development of integrated circuits, laterally diffused metal oxide semiconductor (LDMOS) devices are widely used in switching devices of the home appliances, automotive electronics, medical, and military electronics. For this type of LDMOS, the higher breakdown voltage (BV) and the lower Rdson have always been the ultimate goals.
A conventional method for manufacturing a N trench LDMOS includes the following steps:
A pad oxide layer and a pad silicon nitride are firstly grown using a furnace tube, a photoresist is then coated, which is exposed by using a drift region photomask to define a drift pattern. The pad silicon nitride is removed using etching technology under the protection of the photoresist. Ion implantation is performed to the drift region to adjust the ion concentration of the drift region. After the photoresist is removed, an oxide layer with a predetermined thickness is grown in the furnace tube using the pad oxide layer and the pad silicon nitride as the mask, the pad oxide layer and the pad silicon nitride are then removed. After that, implantation concentration adjustment is performed at drift region and drain end using NG photomask, thus forming a concentration transition region.
During the thermal growth of the drift region oxide layer, the impurity ion implanted in the drift region will diffuse outwardly for a distance, as shown in region A of FIG. 1. The concentration of the n-type impurity in this region is relatively low, when the device is turned on, the resistance contributed by this region is high, resulting in a total high Rdson of the device.